The present invention relates to an image forming apparatus.
A conventional image forming apparatus such as a printer, a facsimile, an electro-photography color recording apparatus, and the likes is provided with an image forming unit. In the image forming unit, a charging roller uniformly charges a surface of a photosensitive drum. Then, an LED (Light Emitting Diode) head exposes the surface of the photosensitive drum to form a static latent image thereon. Afterward, a developing roller as a developer supporting member electrostatically attaches a thin layer of toner as developer to the static latent image, thereby forming a toner image. A transfer device transfers the toner image to a sheet as a recording medium, and a fixing device fixes the toner image to the sheet, thereby forming an image.
In the conventional image forming apparatus, a toner supplying roller is provided for supplying toner retained in a main body of the image forming unit or an image forming unit main body to the developing roller. To this end, a supply bias voltage is applied to the toner supply roller to generate a potential difference between the developing roller and the toner supply roller. The supply bias voltage is adjusted to control an amount of toner supplied to the developing roller, thereby adjusting a density of an image formed on the sheet, i.e., an image density (refer to Patent Reference). Further, an amount of toner supplied to the developing roller affecting image quality may also change according to an image forming condition such as an environmental condition where the printer is placed.
Patent Reference: Japan Patent Publication No. 11-305501